This invention relates to vehicular air conditioning systems, and more specifically, to a method and apparatus for removing residual condensate from a heat exchanger used as an evaporator or an evaporator/condenser/gas cooler with a minimum of energy expenditure.
In many vehicular air conditioning installations, the heater core and the evaporator (or if a heat pump system, the evaporator/condenser/gas cooler) are-arranged serially in the direction of air flow. Typically, the planes of the heat exchangers are arranged approximately parallel to one another and in line with one another so that the air, as one of the heat exchange mediums, flows approximately perpendicularly through the two heat exchangers. While this type of arrangement works generally well for its intended purpose, it accentuates the depth of the air conditioning unit in an environment where there are greater constraints on depth than on length.
As a consequence, there have been proposed air conditioning installations wherein the heat exchangers are in a common plane or intersect at an angle. This sort of arrangement has a very compact construction from the depth standpoint which is advantageous for installations in motor vehicles. One such arrangement is shown in a German patent publication DE 195 18 281 A1. One problem that is encountered is caused by moisture, namely condensate, that is formed in the heat exchanger that forms part of a conventional vapor compression air conditioning system or functions as an evaporator/condenser/gas cooler in a heat pump system. When the system is turned on, the condensate may be entrained or evaporate into the air stream and may be deposited on the windshield of the vehicle causing fogging thereof.
To avoid this, after the air is cooled in the heat exchanger, a reheat operation is necessary to lower the relative humidity of the air and conduct dry air to the interior of the vehicle. From the standpoint of energy economy, the reheating operation is undesirable since the entire air stream is cooled in the evaporator with a corresponding energy expenditure, and then is reheated again, using energy.
The specific problem of drying of the heat exchanger core of the evaporator is not addressed in DE 195 18 281 A1. It is possible that an electrical heating element is arranged before the evaporator for this purpose. However, using an electrical heater to achieve drying requires a corresponding utilization of electrical energy as does the initial heating of the air itself. Frequency, neither is desirable and in the arrangement illustrated in the German patent publication, fan air first flows through the evaporator and then optionally through a heater core.
Use of electrical heating to accelerate drying of the evaporator in such a system is known from German patent publication DE 197 31 369 C1 in which the evaporator and heater are arranged serially in the direction of air flow. Consequently, depth of the unit is relatively great. The unit can but does not necessarily have to operate utilizing a reheat operation with initial cooling of the evaporator air and then reheating it again. In the reheat operation, the surface of the evaporator becomes wet and when the air conditioning operation is initiated subsequent to that, the moisture in the evaporator enters into the inside of vehicle and can lead to fogging of the windows. In this construction, the necessity of drying the evaporator is signaled by a sensor and the electrical heater arranged before the evaporator energized, which has an adverse effect on energy consumption.
In order to minimize energy consumption, it has been known to utilize a heat pump in the air conditioning installation where the heat exchanger is alternatively used as either an evaporator or as a condenser or gas cooler. When switching functions from evaporator operation to condenser or gas cooler operation, it is important to dry the heat exchanger core to minimize the amount of moisture in the air that flows through it. A goal of the invention is to accomplish that with a minimum energy expenditure.
It is a principal object of the invention to provide a new and improved air conditioning system for utilization in a vehicle. More specifically, it is an object of the invention to provide such an air conditioning system that has a minimum depth for ease of installation and/or requires a minimum input of energy to operate it. It is also a primary object of the invention to provide a new and improved method of operating an air conditioning system intended for use in a vehicle.
An exemplary embodiment of an air conditioning system achieving the foregoing objects includes a heater core having an air side and a coolant side in heat exchange relation with one another. The coolant side is adapted to receive liquid coolant from a propulsion source or the like, typically, but not always, an internal combustion engine. A refrigerant heat exchanger is also provide and has an air side and a refrigerant side in heat exchange relation with one another. The refrigerant side is adapted to be connected in a vapor compression cooling system or in a heat pump system to receive a refrigerant therefrom. The heater core and the heat exchanger are in end to end relation and at an angle to one another. The angle is in the range of an acute angle to about 180xc2x0. A housing is provided to contain the heater core and the heat exchanger and the housing includes an air inlet, a conditioned air outlet adapted to discharge conditioned air into a vehicle compartment, a windshield outlet adapted to direct conditioned air to the windshield of a vehicle, and a moist air outlet adapted to discharge moist air from a vehicle. A first flow control vane is located in the housing and is operable to (a) prevent or (b) allow direct air flow from the inlet to the heat exchanger. Also included is a second flow control vane in the housing operable to (a) prevent air flow from the inlet through the heater core or (b) allow air flow from the inlet through the heater core to the heat exchanger and the moist air outlet. A third flow control vane is provided in the housing and is operable to (a) open or (b) close the moist air outlet while a fourth flow control vane is located in the housing for (a) opening or (b) closing the conditioned air outlet. A fifth flow control vane is located in the housing and is operable to (a) open or (b) close the windshield outlet.
As a result of the foregoing construction, when the first vane prevents direct air flow to the heat exchanger and the third vane is operated to open the moist air outlet, the second vane may be caused to allow air flow from the inlet through the heater core to be heated therein and then through the heat exchanger to evaporate any residual condensate thereon and then provide air flow to the moist air outlet to discharge through such outlet to avoid any flogging of the windshield or other windows in the vehicle.
In a preferred embodiment, the second vane is located within the housing to direct air passing through the heater core at the heat exchange air side when the second vane is operated to allow air flow from the inlet through the heater core to the heat exchanger.
A preferred embodiment contemplates that the first and second vanes be movably mounted within the housing on opposite sides of the heater core and the heat exchanger. In a highly preferred embodiment, the first and second vanes are pivotally mounted on axes defining a plane extending approximately between the heater core and the heat exchanger.
In a preferred embodiment, the moist air outlet is in close proximity to the heat exchanger in the direction of air flow through the heat exchanger air side when the second vane is operated to allow air flow from the inlet through the heater core to the heat exchanger and when the first vane is operated to prevent direct air flow from the inlet to the heat exchanger.
In one embodiment of the invention, the heat exchanger is adapted to be connected to a heat pump system and is further adapted to function alternatively as an evaporator or as a condenser/gas cooler.
Preferably, the inlet includes a fresh air port and a passenger compartment port with a sixth flow control vane associated with both of the ports and operable to control the quantity of air entering both of the ports. A fan is disposed within the housing and located downstream of the ports and upstream of the heater core and the heat exchanger.
A highly preferred embodiment contemplates that the heater core be located closer to the ports than the heat exchanger and that the heat exchanger be located closer to the moist air outlet than the heater core.
As alluded to previously, the invention also contemplates a method of operating an air conditioning system. Specifically contemplated is a method for drying the surface of a heat exchanger in a vehicular heat pump air conditioning system and having a moist air outlet and a heater core connected to receive hot coolant from a propulsion source for the vehicle. The method includes the steps of (a) operating the heat pump air conditioning system to cause the heat exchanger to function as a condenser/gas cooler and (b) directing air with a fan first through the heat core and then through the heat exchanger to the moist air outlet.
In a preferred embodiment, steps (a) and (b) are performed after the propulsion source is turned off, and a coolant pump is operated to cause coolant flow through the heater core after the propulsion source is turned off. Thereafter, the method contemplates turning off the coolant pump and the fan.
In a highly preferred embodiment of the method, the coolant pump is turned off shortly before or substantially simultaneously with the turning off of the fan.
Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.